N-Acyl amino acid surfactants are widely used in personal care applications in addition to the other industrial applications. They fall in the category of anionic surfactants and are significantly milder than the rest of the anionic surfactants. For example, surfactants like sodium lauroyl sarcosinate, sodium myristoyl sarcosinate, sodium cocoyl glycinate, sodium cocoyl N-methyl taurate are commercially used in face washes, body washes since they exhibit good cleansing power and are milder to skin and hair compared to other anionic surfactants. Alkanoyl sarcosinates find applications in mouth washes and in dentifrices, in general, due to their bacteriostatic activity. There are a host of other areas where N-acylated amino acids are commercially used such as in petroleum products, as lubricants, in metal processing and ore floatation. (N-acylated amino acid as surfactants, J. D. Spivack, Chapter 16, in ‘Anionic surfactants, Vol 7, Surfactant Science Series, Edited by W. M. Linfield). Commercially, they are manufactured from a two-step synthesis that involves fatty acid and various amino acids such as glycine, sarcosine, N-methyl taurine, alanine, aspartic acid, glutamic acid, glutamine and arginine. These are some of the most commonly used amino acids that are used to manufacture N-acyl amino acid surfactants. However, virtually all amino acids, chiral or racemic, natural or synthetic can be used in the manufacture of N-acyl amino acid surfactants. Also, amino acids used in the surfactant manufacture do not have to be α-amino acids. Also, the acid group in these amino acids can be any other acidic group other than the carboxylic group. Amino sulphonic acids (e.g. N-methyl taurine) have been condensed with fatty acid chlorides and to create commercial surfactants such as sodium N-methyl-N-cocoyl taurate. In the manufacture N-acyl amino acid surfactants fatty acid or a mixture of fatty acids is reacted with amino functionality of amino acids through the intermediacy of fatty acid chloride under typical Schotten Baumann conditions as shown in scheme 1 (U.S. Pat. No. 2,790,7799 (1953), U.S. Pat. No. 2,790,779 (1957), U.S. Pat. No. 3,945,931 (1974)).

Schotten Baumann condensation between fatty acid chloride and an amino acid is typically done in aqueous medium, however, use of mixed solvent systems (solvent and water) is also reported (U.S. Pat. No. 6,703,517 (2002), U.S. Pat. No. 6,569,829 (1999), US Appl. Pub. No 2005/0085651 (2004) and WO2009/065590 (2009)). A few other patents teach about preparation and purification of N-acyl amino acid surfactants that are essentially made by following the same route of condensing fatty acid chloride with amino acids (JP Pat No 2923101 (1991), JP Appl Pub No 04-149163 (1990), JP Pat No 3362468 (1993)).


The precursors of N-acyl amino acid surfactants, the fatty acid chlorides, industrially, are manufactured by reacting fatty acids and a halogenating agent, either phosgene or thionyl chloride as depicted in schemes 2 and 3. The chlorination is usually catalyzed by N, N-dimethyl formamide (DMF). DMF or similar substituted formamides form a complex (Vilsmeier complex) with COCl2 or SOCl2 which is the actual catalytic species (U.S. Pat. No. 5,430,186; U.S. Pat. No. 5,623,082; U.S. Pat. No. 5,200,560; U.S. Pat. No. 5,278,328 & U.S. Pat. No. 5,166,427) in chlorination of acids.
